The present invention is directed to improvements to bar feeding apparatus employed to feed elongate bar stock to a machine tool. In a typical application, the tool will form or otherwise perform an operation upon a relatively short length of the bar, cut off this short length from the bar and eject the formed piece, at which time the feed apparatus will again advance the bar into the tool. When all of the parts which can be formed from a single length of stock have been formed, a remnant will remain with the pusher and is carried by the pusher on its return stroke to an ejecting station at which the remnant is ejected and a fresh length of stock placed in front of the pusher to repeat the feeding cycle.
Many examples of this particular type of feeding apparatus are found in the prior art. See, for example, U.S. Pat. Nos. 3,066,806; 3,582,000; 3,612,298 and 3,924,494. Typically, in these prior art feeding apparatuses, the end of the bar remote from the tool is seated in a resilient split socket or collet which is in turn coupled to one run of an endless cable or chain employed to drive the pusher in the feeding and return strokes. During or prior to the cutting off of the part from the bar by the machine tool, the bar will normally be gripped or chucked by the tool and rotated; hence, the collet must be mounted for rotation relative to the structure employed to couple it to its drive chain or cable.
The grip of the collet upon the stock remnant must be firm enough to retain the stock remnant in the collet during the return stroke of the pusher, but not too firm to interfere with the action of the remnant ejection mechanism which typically takes the form of clamping jaws which are actuated to close upon the remnant as it passes the ejection station and pull the remnant from the collet as the pusher continues along its return stroke.
The collet is subjected to hard usage and requires frequent replacement which imposes practical cost limitations upon its production. As a result, the resilient gripping force of the collet as theoretically calculated by its designer is not always achieved in the collet as manufactured. Attempts to adjust this gripping force subsequent to the manufacture of the collet normally require heating of the collet and expanding or contracting the collet jaws to decrease or increase the gripping force in a trial-and-error process in which the collet must be cooled between each trial.
In addition to the difficully in regulating the gripping force in the initial manufacturing process, the stock handled by the collet is normally not formed to highly precise dimensional tolerances, and oversized pieces forced too deeply into the collet's socket may spring the collet beyond its elastic limit with a consequent reduction in gripping force.